OTA - Operational Transconductance Amplifiers

I've been building a Jasper wasp lately and been wondering why the filter sounds so darn good.
I never really studied the circuit till recently so always assumed it was a completely digital design.
It uses a cmos 4069.... its an inverter... but the other part of the circuit is a
CA3080 ... a OTA...Operational Transconductance Amplifier. This is used instead of your standard Op-amp.
I'm sure this is a big part of the sound.

So what is a OTA?
It's a amplifier unlike your standard Op-amp.

What the OTA  shares with your common Op-Amp is:
1. a single output.
2. They both have inverting & non-inverting inputs.
3. They both have power lines (V+ & V-)

What makes the OTA different is that it has 2 extra inputs (Ibias & Iabc)
and it's output is a current not a voltage.
So, to put it another way, a OTA is a voltage to current amplifier or a voltage controlled current source.

The OTA can also be viewed as an ideal transistor. 

Like a transistor,it has three terminals—
a high impedance input(base)
a low-impedance input/output (emitter)
a current output (collector). 

There are loads of circuits that use the OTAs like VCOs, filters, VCAs, waveshapers. 

OTA's include:
CA3080 (discontinued)
LM13600 - Texas Instruments (formerly National Semiconductor)
LM13700 - Texas Instruments (formerly National Semiconductor)
MAX435 (obsolete product)
MAX436  (obsolete product)
OPA860 -- Texas instruments (SOIC)
OPA861 -- texas instruments
NE5517 - ON Semiconductor
NJM13660 - New Japan Radio (JRC)
NJM13700  - New Japan Radio (JRC)
V13700 - CoolAudio
BA662A  Roland (manufactured by Rohm in the 1970s)*
BA 662B - Roland (manufactured by Rohm in the 1970s)
IR3109
BA6110  - Rohm

* The BA662A is the VCA used in the SH101, TB303, Juno-60, JX-3P, etc etc.
   It's used for portamento in the Jupiter 4.
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CA3080
Lots of old synths use the CA3080 which is obsolete and can be expensive to buy on the second hand market.

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LM13700
The LM13700 is basically two CA3080s on one chip. You can also get these in a DIP (through hole) format. There are also conversion circuits that allow you to use a LM13700 in place of the CA3080.

There are lots of manufacturers still making this useful chip. They may have different part numbers, but the design is still the same one designed by Bill Gross & Don Sauer of  Texas Instruments (formerly National Semiconductor).

Here is the pinout for a LM13700

We basically have 2 identical op-amps.
This is really good for circuits that require matched pairs of amps.

Pin1
Amplifier Bias input
This sets the level of transconductance.
(the relation between the output & input current).

Pin2
Diode Bias A
Current applied here allows the chip to accept a higher differential input voltage.
This will improve linearity & distortion.

Pin3
Non-inverting input A

Pin4
Inverting Input A

Pin5
Output A
The output of the opamp as a current.
This equals the difference in input voltage  between pin 3 & 4 , multiplied by the transconductance.

Pin6
-V

Pin7
Buffer input A
Darlington pair buffer

Pin8
Buffer output A
Darlington pair buffer
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Links
Comparing BA662A with BA6110 VCA chips in the x0xb0x 

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If there are any mistakes, omissions or if this is just BS please let me know.